WHy would it be hard to do a game based on both the quality of land and what civs can trade?
Because what matters is relative value. If economy value is nearly all dependent on land, then the difference between city sites matters a lot.
But if trade is a major part of the economy, and you can get a high trade value anywhere no matter, then the value of getting good land is less important.
You can't have everything be important, because importance as a concept is only defined relative to the rest of the model.
Land is an important factor in determining economy in Civ, because it matters more than other factors.
To try to give some practical demonstration of what I mean:
Imagine a version A of civilization. A is the same as Civ4, except that the commerce values from trade are 10x higher.
What this means is that terrain is relatively less important than in Civ4. The extra +3 commerce or so you get from having some river tiles in your BFC really don't matter, because *any* city can generate 30-40 commerce no matter where it is built. So a river city might have 33-43 commerce, whereas a non-river city might get 30-40 commerce.
In contrast, consider a version B of civilization. B is the same as Civ4, except that tiles adjacent to rivers give +10 commerce each.
What this means is that trade is relatively less important than in Civ4. All that really matters in terms of powering your economy is how many river tiles you control.
This is my point; you have a total economy size, that is driven by a number of factors. What matters in strategic terms is the relative dependence of your total economy size (ie commerce per turn) on the various input factors (trade routes, rivers, bonus resources, etc.)
Or similarly; imagine version C of Civ4, which was exactly the same as Civ4 except that all tiles yielded an additional 6 food. What this would mean is that food resources like wheat and rice were less valuable, even though they produced the same extra food yield, because food would no longer really be much of a constraint, and you can get high food yields from any tile.
Is that inherent to the system of civ
It is inherent to the design of an economy model, like that in a computer game or any other kind of economy model.
What I do not understand is how in real life an economy is 'based on land.'
Think Jared Diamond, and Guns Germs and Steel. He has a geographic view of history. Eurasia became the dominant powers in history (rather than Africa or the Americas or Australia) because they had better natural resources; better climate, better wild crops, better wild animals more suitable for domestication, and so forth. And that it was these advantages that then led to technological advantages, military advantages and allowed them to colonize the world.
This is say in contrast to an institutional model of economies and history, which might say that Europe became the dominant power because European countries had better political and economic institutions that fostered economic technological development or a "better" religion.
Or a racial/genetic version of history, which says that Europe became dominant because white people are intrinsically smarter and better than native americans or africans.
[Obviously this one is wrong and pretty offensive, but many people believed it once upon a time, and a few crazies still do.]
"Civilization has a geography-based view of human history and a technological view, rather than an institutional or cultural one" I think a reality check is in order.
What I mean is this; when designing a game based on history, you have do decide which view of history you're going to take.
Civ follows a traditional-land-based model of city formation and civilization. The first cities show up in areas with high agricultural food yields. City growth is driven primarily by food supplies. Different "quality" of land and access to quality bonus resources are major drivers of civilization. Specialists come from having excess food supply, and these are what drive history's Great People.
Institutions don't matter nearly as much; technology is driven primarily by economic output from land. If you're a civ with a bad land start position or expansion areas, then you're pretty much doomed to be backwards forever.
get some perspective - and some fresh air...
Bit patronizing, don't you think?